i
20
24
DIGITAL
COMMUNICATION
LAB MANUAL
BECL
504
DEPARTMENT OF
ELECTRONICS
&
COMMUNICATION
ENGINEERING
CITY
ENGINEERING
COLLEGE
i
Communication
Laboratory
The Communication Laboratory covers design and verification of the concepts of modern digital
communication systems that operates from MHz
-
GHz range. The lab include experiments on
applications of Digital coding and modulation techniques, Fiber Optic Commu
nication, and
Characteristics of microwave waveguide components. This lab is equipped with Oscilloscopes,
Function Generators, Modules for Digital Modulation and Demodulation techniques and Power
Supply units.
To enhance precise measurement and observe waveform with better clarity Digital Storage
Oscilloscopes are used. The Microwave test benches are used to conduct experiments in GHz
frequency range. Various digital coding and modulation kits are used apart fro
m discrete
components to demonstrate the basic concepts involved in digital communication. An OFT kit is
used to demonstrate communication and multiplexing through Light waves.
ii
Digital
Communication
Lab
Semester
5
Course
Code
BECL504
CIE
Marks
50
Teaching
Hours/Week
(L:T:P:
S)
0:0:2:0
SEE
Marks
50
Credits
01
Total
SEE+CIE
100
Exam
Hours
2
Hours
Examination
type
(SEE)
Practical
Course
objectives:
This
laboratory
course
enables
students
to
•
Design
of
basic
digital
modulation
techniques
using
electronic
hardware.
•
Simulation
of
vector
computations
and
derive
the
orthonormal
basis
set
using
Gram
Schmidt
procedure.
•
Simulate
the
digital
transmission
and
reception
in
AWGN
channel
•
Simulate
the
digital
modulations
using
software
and
display
the
signals
and
its
vector
representations.
•
Implement
the
source
coding
algorithms
using
a
suitable
software
platform.
•
Simulate
the
channel
coding
techniques
and
perform
decoding
for
error
detection
and
correction.
Sl.NO
Experiments
Hardware
Experiments
1
Generation and
demodulation
of
the Amplitude
Shift Keying
signal.
2
Generation
and
demodulation of
the
Phase
Shift Keying
signal.
3
Generation
and
demodulation
of
the Frequency
Shift
Keying
signal.
4
Generation
of
DPSK
signal
and
detection
of
data
using
DPSK
transmitter
and
receiver.
Simulation
Experiments
(Use
MUKU:GO
/
MATLAB
/
Scilab
/LabVIEW
or
any
other
suitable
software)
5
Gram
-
Schmidt
Orthogonalization:
To
find
orthogonal
basis
vectors
for
the
given
set
of
vectors
and
plot
the
orthonormal
vectors.
6
Simulation of binary
baseband
signals
using
a
rectangular pulse and
estimate the BER
for AWGN
channel
using matched
filter receiver.
7
Perform
the
QPSK
Modulation
and
demodulation.
Display
the
signal
and
its
constellation.
8
Generate
16
-
QAM
Modulation and
obtain
the QAM
constellation.
9
Encoding
and
Decoding of Huffman
code.
10
Encoding
and
Decoding
of
binary
data
using
a
Hamming
code.
11
For
a
given
data,
use
CRC
-
CCITT
polynomial
to
obtain
the
CRC
code.
Verify
for
the
cases,
a)
Without
error
b)
With
error
12
Encoding
and
Decoding
of Convolution
code
Sl.
No.
Name
of
the
Experiment
1
Generation and
demodulation
of
the Amplitude
Shift Keying
signal.
2
Generation
and
demodulation of
the
Phase
Shift Keying
signal.
3
Generation
and
demodulation
of
the Frequency
Shift
Keying
signal.
4
Gram
-
Schmidt
Orthogonalization:
To
find
orthogonal
basis
vectors
for
the
given
set
of
vectors
and
plot
the
orthonormal
vectors.
5
Simulation of binary
baseband
signals
using
a
rectangular pulse and
estimate
the BER
for AWGN
channel using matched
filter receiver.
6
Perform
the
QPSK
Modulation
and
demodulation.
Display
the
signal
and
its
constellation.
7
Generate
16
-
QAM
Modulation and
obtain
the QAM
constellation.
8
Encoding
and
Decoding of Huffman
code.
9
Encoding
and
Decoding
of
binary
data
using
a
Hamming
code.
10
Encoding
and
Decoding
of Convolution
code.
Digital Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
AIM:
To design and study the working of ASK modulation and demodulation system with the help of
suitable circuit Specifications: M(t) = 10V, 500Hz
, C(t) = 5V, 10KHz.
COMPONENTS
REQUIRED:
Sl.
No.
Item
&
Specification
Quantity
1
Transistor
-
SL100
1No.
2
uA741
2
No.
3
Resistor
-
6.8K
1
No
4
Resistor
-
2.2K
1No.
5
Resistor
-
22k pot
1
No.
6
Capacitor
-
0.01u
F
1No.
7
Diode
-
1N
4001
1No
.
THEORY:
Amplitude Shift Keying (ASK) is a digital modulation scheme where the binary data is
transmitted using a carrier signal with two different amplitude levels. For binary 0 and 1, the
carrier switches between these two levels. In its simplest form, a carrier
is sent during one input
and no carrier is sent during the other. This kind of modulation scheme is called on
-
off keying.
A simple ASK modulator circuit is shown in figure. Here a sinusoidal high frequency
carrier signal is sent for logic ‘0’ (
-
5V) and no carrier is sent for logic ‘1’ (+5V). The transistor
works as a switch closes when the input (base) voltage is +5V (logic ‘
1’) and shorts the output.
When the input voltage is
-
5V (logic ‘0’), the switch opens and the carrier signal is directly
connected to the output.
The demodulator circuit consists of an envelope detector and a comparator. The diode
D selects the positive half cycle of the ASK input. The envelop detector formed by 2.2K resistor
and 0.01uF capacitor detects the data out of the ASK input. The Op Amp com
parator and the
zener diode amplitude limiter convert this detected signal to its original logic levels. The 10K
potentiometer may be varied to set suitable reference voltage for the comparator.
Expt
No
-
1
.
AMPLITUDE
SHIFT
KEYING
MODULATION
AND
DEMODULATION
Digital Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
CIRCUIT
DIAGRAM:
EXPERIMENTAL
PROCEDURE:
1.
Rig
-
up
the
modulator
circuit
as
show
in
the
figure.
2.
Set
the message
signal
of
amplitude
10
V(P
-
P)
and
frequency
500
Hz.
3.
Set
the
carrier
signal
of amplitude
2
V(P
-
P)
and
frequency
2
kHz.
4.
Observe both the message input and ASK output
simultaneously on CRO and plot.
5.
Apply the ASK output of the modulator to the demodulator input.
6.
Observe both the ASK input and the demodulated output simultaneously on CRO.
Adjust the reference voltage of the comparator if needed.
7.
Plot the
waveforms.
Digital Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
OBSERVATIONS:
EXPECTED
WAVEFORMS:
RESULTS
:
ASK
is generated and verified using modulation and demodulation
techniques
.
Time Period
Amplitude
Messages
Carrier
Output Signal
Demodulated Signal
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
AIM:
To study the working of FSK modulation and demodulation with the help of a suitable circuit.
Specifications:
M(t) = 10V, 500Hz , C1(t) = 5V, 1KHz. C2(t) = 5V, 2KHz.
COMPONENTS
AND
EQUIPMENTS
REQUIRED:
Sl.
No.
Item
&
Specification
Quantity
1
Transistor
-
SL100
, SK100
1No.
2
uA741
2
No.
3
Resistor
-
10K
1
No
4
Resistor
-
1
.5
k
1No.
5
Resistor
-
22k pot
1
No.
6
Capacitor
-
0.
1
u
F
2
No.
7
Diode
-
1N
4001
1No
.
THEORY:
Frequency Shift Keying (FSK) is a digital modulation scheme where the
digital data
is transmitted using a high frequency
carrier signal. For logic ‘0’ and ‘1’ the carrier signal
switches between two preset frequencies, hence the name FSK.
Binary FSK is a form of constant
-
amplitude angle modulation and the modulating signal is a
binary pulse stream that varies between two discreate voltage levels but not continuous
changing analog signal. In FSK, the carrier amplitude
(Vc) remains constant with modulation
and the carrier radian frequency(wc) shifts by an amount equal to +w/2. The frequency shift
is proportional to the amplitude and polarity of the input binary signal. For example, a binary
1 could be +1 volt and a binar
y zero could be
-
1 volt
producing frequency shifts of +delta(w)/2
and
–
delta(w)/2 respectively. The rate at which the carrier frequency shifts is equal to the rate
of change of the binary input signal vm(t). thus the output carrier frequency deviates(shifts)
between wc+delta(w)/
2 and wc
-
delta(w)/2 at the rate equal to fm.
Expt
No
-
2
.
FREQUENCY
SHIFT
KEYING
MODULATION
&
DEMODULATION
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
CIRCUIT
DIAGRAM:
EXPERIMENTAL
PROCEDURE:
1.
Test
all
the components
and
probes.
2.
Set
up
the
FSK
modulator
and
demodulator
circuits
on
the
bread
board.
Switch
on
the power
supplies.
3.
Feed
5V,
100Hz (10Vpp, 100Hz)
square
wave
as
the
data
input.
Vary
the
pot R
C
to
adjust the
output frequencies if needed.
4.
Observe
both
the
input
and
output
waveforms
on
CRO
and
plot.
5.
Apply the FSK output of the modulator to the input of the demodulator, and observe the output.
Vary
the
10K
pot to
get
the
PLL
locked
with
the
input
signal. Plot
the
waveforms
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
EXPECTED
WAVEFORMS:
OBSERVATIONS:
RESULTS
:
FSK is verified using modulation and demodulation technique.
Time Period
Amplitude
Messages
Carrier
Output Signal
Demodulated Signal
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
AIM:
To Study the operation of PSK ( Binary) modulation & Demodulation and to plot
the PSK wave
forms for Binary data at different frequencies.
COMPONENTS
AND
EQUIPMENTS
REQUIRED:
Sl.
No.
Item
&
Specification
Quantity
1
Transistor
-
SL100
1No.
2
uA741
3No.
3
Resistor
-
10K
5No
4
Resistor
-
1k
–
1
1No.
5
Resistor
-
10k pot
1No.
6
Resistor
-
22k pot
2No.
7
Capacitor
-
1
0u
F
1No.
8
Diode
-
1N
4001
1No
.
THEORY:
Phase Shifting Keying (PSK) is a modulating / Data transmitting technique in which
phase
of
the
carrier
signal
is
shifted
between
two
distinct
levels. In
a simple
PSK
(i.e
Binary PSK) un
-
shifted carrier is
transmitted to indicate a 1 condition , and the carrier shifted by
180
o
i.e
is transmitted to indicate a 0
condition. Wave forms
are shown in Figure PSK Modulating & Demodulating circuitry can be developed
in number of ways, one of the simple circuit is used in this trainer.
Expt
No
-
3.
PHASE
SHIFT
KEYING
MODULATION
&
DEMODULATION
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
EXPERIMENTAL
PROCEDURE:
1.
Connect carrier signal to carrier input of the PSK Modulator.
2.
Connect data signal say 4 KHz from data source to data input of the modulator.
3.
Keep CRO in dual mode.
4.
Connect CH1 input of the CRO to data signal and CH2 to the output of the PSK
modulator
5.
Observe the PSK o/p Signal with respect to data signal and plot the wave forms
6.
Compare the plotted waveforms with given wave forms.
7.
Connect
the
PSK output
to the PSK
input of the
demodulator.
8.
Connect
carrier
to
the carrier
input
of
the
PSK
demodulator
9.
Note:
In actual communication
system
reference
carrier
is generated
at
receiver.
10.
Keep
CRO
in
dual
mode.
11.
Connect
CH1
to
the
data
signal
(at
Modulator)
and
CH2
to
the
output
of the
demodulator.
CIRCUIT
DIAGRAM:
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
Simulation
Experiments
(Use
MUKU:GO
/
MATLAB
/
Scilab
/LabVIEW
or
any
other
suitable
software)
4
Gram
-
Schmidt
Orthogonalization:
To
find
orthogonal
basis
vectors
for
the
given
set
of
vectors
and
plot
the
orthonormal
vectors.
5
Simulation of binary
baseband
signals
using
a
rectangular pulse and
estimate the BER
for AWGN
channel
using matched
filter
receiver.
6
Perform
the
QPSK
Modulation
and
demodulation.
Display
the
signal
and
its
constellation.
7
Generate
16
-
QAM
Modulation and
obtain
the QAM
constellation.
8
Encoding
and
Decoding of Huffman
code.
9
Encoding
and
Decoding
of
binary
data
using
a
Hamming
code.
10
Encoding
and
Decoding
of Convolution
code
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
4
Gram
-
Schmidt
Orthogonalization:
To
find
orthogonal
basis
vectors
for
the
given
set
of
vectors
and
plot
the orthonormal
vectors.
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
OUTPUT
:
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
5
Simulation of binary baseband signals using a rectangular pulse and estimate the BER
for AWGN channel using matched filter receiver.
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
OUTPUT:
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
6
Perform the QPSK Modulation and demodulation. Display the signal and its
constellation.
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
OUTPUT
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
7
Generate
16
-
QAM
Modulation and
obtain
the QAM
constellation.
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
OUTPUT:
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
8
Encoding and Decoding of Huffman code.
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
OUTPUT:
Enter the probabilities:
[0.3 0.25 0.2 0.12 0.08
0.05]
The huffman code dict:
[1] '0 0'
[2] '0 1'
[3] '1 1'
[4] '1 0 1'
[5] '1 0 0 0'
[6] '1 0 0 1'
Enter the symbols between 1 to 6 in[
]:
[3]
sym =
3
The encoded
output:
1
1
Enter the bit stream in[
];
[1 1]
The symbols are:
3
Entropy is 2.360147 bits
Efficiency is:0.991659
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
9
Encoding
and
Decoding
of
binary
data
using
a
Hamming
code.
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
OUTPUT:
Digital
Communication
Lab
Manual
-
BECL504
Dept
of
E&C,
CITY
ENGINEERING
COLLEGE
1
0
Encoding
and
Decoding
of Convolution
code
OUTPUT:
Message Sequence:
1 0 1 1 0
Encoder output:
1 1 1 0 0 0 0 1 0 1
Decoder output:
1 0 1 1 0